Cracking by thermal hydrode-polymerization

ABSTRACT

HYDROCARBON RESIDUA BOILING MOSTLY 1000*F. AND ABOVE ARE DEPOLYMERIZED IN THE PRESENCE OR ABSENCE OF HYDROGEN IN ONE OR MORE STAGES UNDER LIQUID PHASE CONDITIONS TO OBTAIN A PRODUCT WHICH IS PREDOMINANTLY AN AROMATIC GAS OIL AND EMINENTLY SUITABLE EITHER AS A SOLVENT OR AS FEED TO HYDROCRACKING OPERATIONS. ALTHOUGH THE UPPER BOILING LIMIT OF THIS GAS OIL MAY BE IN THE RANGE OF 600 TO 1000*F., THE PROCESS IS ILLUSTRATED BY TWO SCHEMES, ONE IN WHICH THE GAS OIL IS SEPARATED INTO FRACTIONS BOILING 430-650* F., 650-1000* F. AND 1000* F.+ AND THE OTHER IN WHICH THE GAS OIL IS SEPARATED INTO 430-650* F. AND 650* F. + FRACTIONS. IN EACH SCHEME AN AMOUNT OF THE LOW-BOILING FRACTION IS RECYCLED SO THAT THE FEED MIXTURE TO THE REACTION ZONE CONTAINS 20 TO 50% OF THE LOW-BOILING FRACTION WHILE THE HIGH BOILING FRACTION IS RECYCLED AT A RATE SUCH THAT THE AMOUNT PRESENT IN THE FEED MIXTURE TO THE REACTOR IS EQUAL TO THE AMOUNT IN THE MAKE PRODUCT THUS RESULTING IN BALANCED CONDITIONS. 1-25% OF AN ACYCLIC HYDROCARBON MODIFIER AND/OR A MILD ALKALI IS ADDED TO THE REACTION MIXTURE TO ACT AS A FREE-RADICAL ACCEPTOR. WHEN A HYDROCARBON IS USED IS HAS A RESIDENCE TIME OF ONE HOUR OR LESS AS COMPARED TO 1 TO 6 HOURS FOR THE RESIDUA-CYCLE MIXTURE.

June 18, 1974 R. B. MASON ETAL 3,817,854

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United States Patent Int. Cl. Cg 37/02 US. Cl. 208-59 19 Claims ABSTRACTOF THE DISCLOSURE Hydrocarbon residua boiling mostly 1000 F. and aboveare depolymerized in the presence or absence of hydrogen in one or morestages under liquid phase conditions to obtain a product which ispredominantly an am matic gas oil and eminently suitable either as asolvent or as feed to hydrocracking operations. Although the upperboiling limit of this gas oil may be in the range of 600 to 1000 F., theprocess is illustrated by two schemes, one in which the gas oil isseparated into fractions boiling 430-650 F., 6501000 F. and 1000" F.+and the other in which the gas oil is separated into 430-650 F. and 650F fractions. In each scheme an amount of the low-boiling fraction isrecycled so that the feed mixture to the reaction zone contains 20 to50% of the low-boiling fraction while the high boiling fraction isrecycled at a rate such that the amount present in the feed mixture tothe reactor is equal to the amount in the make product thus resulting inbalanced conditions. 1-25% of an acyclic hydrocarbon modifier and/or amild alkali is added to the reaction mixture to act as a free-radicalacceptor. When a hydrocarbon is used it has a residence time of one houror less as compared to l to 6 hours for the residua-cycle mixture.

RELATED APPLICATIONS This is a division of application Ser. No. 29,629,by Ralph B. Mason and Glen P. Hamner, filed Apr. 17, 1970, now U.S. Pat.3,707,459, issued Dec. 26, 1972; which, in turn, was acontinuation-in-part of application Ser. No. 839,220, by Ralph B. Masonand Glen P. Hamner, filed July 7, 1960, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to the thermalconversion of hydrocarbon residua and more particularly relates to thevisbreaking of heavy residua under conditions of extinction recycle.

It is expected that steam cracking facilities will expand in the future,particularly in Europe. This will require means for easily disposing ofthe considerable amounts of tar which are a concomitant part of thesteam-cracking process. One obvious method is to upgrade these tars aswell as other residues by thermally-treating the tars with a hydrogendonor diluent material. The donor diluent is a hydrogen-containingmaterial, aromatic-naphthenic in nature, that has the ability to take uphydrogen in a hydrogenation zone and readily release it to ahydrogendeficient oil in a thermal cracking zone. Unfortunately,however, there is often undesired coke deposition at hot spots andpreheater zones, leading to plugging of the equipment.

SUMMARY OF THE INVENTION In accordance with this invention the abovedisadvantages are overcome by subjecting hydrocarbon residues boilingmostly 1000 F. and above to thermal depolymerization or visbreaking inthe liquid phase in the presence or absence of hydrogen and in thepresence of a free radical acceptor, such as an acyclic hydrocarbonand/or a mild alkali. One or more stages may be used. In the case ofsingle stage operation a high-boiling material is recycled to extinctionand a low-boiling material is recycled so that the amount recycled plusthat in the feed is maintained between 20 and 50% and preferably atabout 30% of the total composition fed to the reaction zone. The amountof high-boiling material in the recycle and the amount in the productare kept at about the same level, generally leveling off at about 47% soas to maintain balanced conditions. The low boiling material has aboiling range beginning well below 650 F., e.g., 430 F. and ending atleast as high as 650 F. and even as high as 1000 F.

When multistage operation is used the initial stage or stages arecarried out under mild conditions, after which 45-50% of thehigh-boiling product from the initial stage or stages is blended with20-50% of the low-boiling product, based on total blend, anddepolymerized in one or more additional stages under somewhat moresevere conditions. Conversion of the high-boiling fraction from thefirst stage or stages is maintained between 25-40% and in the succeedingstage or stages 2530%.

In this embodiment it is not necessary to operate under balancedconditions in the initial stage. If balanced conditions are maintainedthe high-boiling fraction is recycled to extinction and divided betweenthe stages such that the total recycle from all the stages is equal tothe amount in the feed to the first reactor.

Yields of vol. percent of the low-boiling product can be obtained withsmall losses to gas and coke. The multistage process yields even smallerlosses.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 represents in diagrammatic forma method for carrying out the invention using a single stage.

FIG. 2 represents in diagrammatic form a method for carrying out theinvention in two stages.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, ahydrocarbon residue having a Conradson carbon number between 5 and 40and a substantial amount boiling at 1000 F. and above, such as thermaltar from steam cracking, reduced crude, shale oil residue, liquefiedcoal fractions, and the like is fed by line 1 and mixed with lowerboiling material, such as gas oil, preferably recycled from a laterstage of the process which enters through line 2, mixed with 50-5000s.c.f. of hydrogen or a non-oxidizing gas per barrel of feed from line3. Gas oil or the like acts as a solvent for the tar and permits easypumping at moderate temperatures and prevents coking at hot spots in thesystem. In case the feed material has been stored for sometime or hasotherwise had a chance to pick up small amounts of oxygen, it may bedesirable to subject it to a preliminary deoxygenation step in which itis contacted with a suitable deoxygenation catalyst, such as reducedcopper, nickel or cobalt at a temperature below 700 F, preferablybetween 430 and 650 F. The feed mixture is passed by line 4 into thebottom of depolymerizer or visbreaker 5 where the mixture is maintainedat a temperature of 700-900 F., preferably 750-770 F.) and undersufficient pressure to maintain it in the liquid phase, e.g., 50-1000p.s.i.g. A free-radical acceptor or modifier, preferably an acyclichydrocarbon, which may be a paraffin or iso-parafiin of 4 to 20 carbonatoms per molecule, or an olefin or iso-olefin of 2 to 20 carbon atomsper molecule or mixtures thereof is added by lines 6 and 7. Suitablehydrocarbons include the paraffins n-heptane and n-pentane,2,2,4-trimethyl pentane, the olefins, 2,4,4trimethyl pentene-l, and2,4,4 trimethyl pentene-2, as well as other olefins of similar skeletalconfiguration, low octane unsaturated naphtha fractions, normal C -Cvirgin naphtha, catalytic heavy naphtha, heavy alkylates, a 100-165" F.hydroformate fraction and the 210-400 F. fraction made by polymerizingpropylenes and butylenes with H PO, on kieselguhr [HydrocarbonProcessing, V. 47 :170 (September 1968)]. and the like. Thesehydrocarbons are added in amounts of about I to 25% based on tar feedand are sprayed, jetted or otherwise passed through the liquid tar phasein depolymerizer 5, into the vapor phase and removed overhead throughline 8. The residence time of the modifier added through line 7 shouldrange from about 5 minutes to one hour. The presence of the hydrocarbonmodifiers at such short residence times results in reduced coke and gasloss. However some of the modifier is consumed in the process. Whenn-heptane is the modifier the degradation products are predominantlynormal hydrocarbons, namely, n-butane, npentane, n-hexane, etc. whereaswhen iso-octane is used the degradation products are predominantlybranched, i.e., isobutane, isopentane and branched C and C paraffins.The use of 2,2,4-trimethyl pentane and olefins of a similar skeletalconfiguration results in the production of the important blending agent,triptane. Without intending to limit the invention to any theory of whatoccurs, it is believed that the mechanism is one in which the modifieris being consumed with accompanying hydrogen exchange, demethanation,alkylation, isomerization, aromatic disproportionation and probablyevery known hydrocarbon reaction. The most plausible explanation is afree-radical mechanism in which the condensed ring aromatic componentsof the tar depolymerize with the formation of free-radicals which attachthemselves to the modifier as a sink." In doing so the modifier in turnforms free radicals involving stepwise degradation and rearrangementreactions leading to gaseous products, coke, etc.

From the above it appears that conditions of short residence times forthe modifier (less than one hour) coupled with fairly long residencetimes for the tar feed (one to six hours) is important for best results.

If desired a solid free radical acceptor may be slurried with the feedintroduced through line 1. The alkaline material may be any mild alkalisuch as Na,co,, CaO, Ca('OI-I) Ba(OH) Li CO CaCO- BaCO MgCO Mg(OH)sodalite or the like. When the alkali is added along with thehydrocarbon modifier, it is used in amounts of 0.1 to 1 part by weightof alkali per part by weight of feed. However, if desired, the alkalimay be used alone in which case it is added in amounts of 0.1 to 50weight percent based on feed.

The hydrocarbon modifier leaving depolymerizer 5 through line 8 ispassed to separator 9 from which hydrogen and uncondensed gas isrecycled by line 10. Condensate from separator 9 is passed by line 11 tofractionator 12 from which low boiling products are removed by line 13and unreacted modifier and entrained higher boiling components by line14. This unreacted modifier is recycled to depolymerizer 5 by lines 15and 7.

Liquid products are withdrawn from depolymerizer 5 by line 16 and passedthrough filter 22 where coke and/or other solid contaminants are removedand then passed to flash chamber 17 where they are separated into highand low-boiling products. The cut point between the lowboiling andhigh-boiling products may vary between 650 F. and 1000 F. In oneexample, those boiling below 650 F. are either drawn off as makeproducts through lines 18 and 21 or are recycled to depolymerizer bylines 18, 2 and 4. Products boiling above 650 F. are recycled by lines20, 15 and 7. In another example, the low-boiling products recycledthrough lines 18 and 21 or 18, 2 and 4. boil 1000 F.-. The high-boilingmaterials bo-il above 1000 F.

The amount of low-boiling products recycled by lines 18, 2 and 4 iscritical, and must be between 20 and 50% of the total compositionregardless of the distribution of the other materials. This control ismade possible by withdrawing an amount of low-boiling material from thesystem by line 21 necessary to maintain the proper recycle ratio. Theproduct drawn off through line 21 is suitable as such, as solvent foruse in the chemical industry or may be further fractionated to separateout desired solvent and aromatic fractions and if desired with recycleof the high-boiling material.

The recycle of the high-boiling material on the other hand is controlledso that the amount of this material fed to the depolymerizer based ontotal feed will be substantially the same as the amount of thishigh-boiling material found in the product, based on tar blend.Generally this is between 45 and 50%, preferably 46-47%. While it is notintended to be bound by any theory as to the mechanism involved, it isbelieved that the beneficial results obtained are due to an equilibriumphenomenon in which an equilibrium exists between the condensed ringaromatic-containing high-boiling fraction and the lower boilingdepolymerized fraction. Excessive amounts of the low-boiling fractionwill retard the depolymerization, limit throughput of thedepolymerization feed and incur excessive handling costs.

Referring now to FIG. 2, a hydrocarbon residue having a Conradson carbonnumber between 5 and 40 and a substantial amount boiling 1000 F. andabove, such as thermal tar from steam cracking, reduced crude, shale oilresidue, liquefied coal fractions, and the like is fed by line 101 andmixed with lower boiling material, such as gas oil, preferably recycledfrom a later stage of the process which enters through line 102, mixedwith a mixture of fresh hydrogen or a nonoxidizing gas and a freeradical acceptor from line 103. Recycle hydrogen and free radicalacceptor is introduced into the fresh feed mixture by line 106. The gasoil or the like acts as a solvent for the tar and permits easy pumpingat moderate temperatures and prevents coking at hot spots in the system.The free-radical acceptor or modifier is selected from the same group asdescribed in connection with FIG. 1. The mixture is passed by line 104into the bottom of the first stage depolymerizer or visbreaker 105 wherethe mixture is maintained at a temperature of 700-900 F. (preferably750770 F.), and under sufficient pressure to maintain it in the liquidphase, e.g. 50-1000 p.s.i.g. The residence time of the modifier orfree-radical acceptor added through lines 103 and 106 is directlyproportional to its concentration in the feed. For this reason themodifier is added in amounts of l to 25 wt. percent based on residuafeed. As described in connection with FIG. 1, a mild alkali may beslurried with the feed in the same manner and amounts as theredescribed.

The mixture leaving depolymerizer 105 through line 108 is passed toseparator 109 from which hydrogen and uncondensed gas are passed by line110 to condensor 120 and thence by line 133 to gas separator 121 fromwhich recycle hydrogen and hydrocarbon modifiers are recycled by lines126 and 106. Liquid material from separator 109 is passed by line 111 toflash chamber 112 from which products boiling below about 650 F.including the modifier are removed by line 113 and passed tofractionator 130. A portion of the product from flash chamber 112 whichboils below about 650 F. is withdrawn to storage by line 132. Theseparation in flash chamber 112 is not sharp but is only a roughapproximation so that some high-boiling material is actually takenoverhead through lines 113 and 132.

Products boiling approximately above 650 F. are withdrawn from flashchamber 112 by line 114 and a portion thereof is passed through filter115 where coke and/or other solid contaminants are removed. The locationof the filter is not considered critical since it may be located in line111 leading to flash chamber 112 or it may be in line 108 so that thesolids are removed immediately upon removal from the depolymerizationzones 105 and 117.

The high boiling products passed through filter 115 are taken by line116 to second stage depolymerizer 117 where they are maintained undermore severe conditions than in depolymerizer 105. Rcacted products fromdepolymerizer 117 are removed through line 135 and combined withproducts from depolymerizer 105 flowing in the depolymerizer based ontotal feed will be substantially the same as the amount of thishigh-boiling material found in the product, based on tar blend.Generally this is between 45 and 50%, preferably 46-47%.

In accordance with the embodiment of the present invention utilizing amultistage system, the conversion of the high-boiling material isconducted under mild conditions with only a minimum of coke make in theinitial stage. Thus in order to keep the system in balance with line 108on way to separator 109. 10 no build up of high-boiling material, aportion of the high- The remainder of the products from flash chamber112 boiling material is depolymerized under conditions of flowing inline 114 are taken by line 137 and recycled to greater severity whichinherently results in greater colre depolymerizer 105 by line 102. Theamount of 650 F.+ P1118 gas make, but $11168 y a P of matorlal productthus diverted to depolymerizer 105 is such that p c ss the overall l pgas make'ls s than in the li uid feed to depolymerizer 105 contains 35to 45% a ma Stage y m whi h m t be k p 1 n mpos 1uon f bly 9 recycleproduct d i h m balance for maximum production of low-boil ng fractions.ent containing 45-50% (perferably 46-47%) corresponds The followingexamples are included to illustrate the to conversion of 25-40% of 650F.+ in depolymerizer effectiveness of the Instant P o the po lf f 105.This method of operation results in balanced condition of hydrocarbonl'esldlla, Wlthout however, llmltlng the tions in the combineddepolymerization zones 105 and Same- 117. Thus, it is not necessary toforce balanced conditions EXAMPLE 1 in Smgle Stage f the case ofmultlple stages a A steam cracked tar consisting of 35.7% materialboilport on of the 650 F.-|- product from filter 115 is passed ing 43050 F 343% b li 50 1000 F d 30% y llno to P Y F Zone boiling 1000 F.+ wassubjected to several cycles of hy- Retumulg "9 to fractlonator afractlon bollmg drodepolymerization for four hours each at 765 F. underbelow 400 @P throutfh lme 122 as P 1000 p.s.i.g. hydrogen pressure whileabout 10% n-hepwoofld fraction l g 400-550 or oven "P to 1000 tane,based on tar was thoroughly agitated with the liquid. 18 removed y 11116123 also as p A Pornon of The first cycle was carried out with norecycle and the each of these fraction is recycled by lines 127, 135,118, remainder with varying amounts of recycle of the 650 and 102 backto depolymerization zone 105. Another por- F. and 650 F.+ fractions. Thefollowing data were tion, if balanced conditions are maintained, ispassed by obtained:

Cycle 1 2 3 4 5 6 7 Grams tinfeed 565 438 526 654 415.5 343.4 455.5 Feedcomposition, wt. percent:

Fresh tar 106 46.1 40.9 35.7 39.1 32.8 36.1 430650 F. recycle 0 20.619.1 13.1 20. 84.0 18.0 650 F.+ reeyc e 0 39.5 as .4 46.2 40.2 33.2 45.6Total 430-650 F. content--- .1 34.1 34.2 36.8 54.5 45.6 36.1 656 F.+content 64.3 65.6 65.8 59.2 65.5 54.4 69.3 Product yields, based on tar,

wt. percent:

650 F.+ 40.6 47.2 46.6 41 46.5 39.3 45.8 Coke plus gas 0 2.9 2.5 4.7 0.83.2 4.2

1 Corrected by amount or n-heptane lost.

I 430-650 F. recycle from previous cycles. Recycle material in cycles 2and 8 from similar operation but with catalyst.

I 221-650 F. recycle.

lines 127, 135, and 134 to filter 115 thence through line 116 todepolymerizer 117 where in conditions of greater severity, e.g.temperatures between 750 and 950 F. (preferably 775-800 F.) aremaintained. However the same conditions may be maintained in bothdepolymerizers 105 and 117, in which case the residence time is longerin depolymerizer 117 than in depolymerizer 105.

Fresh hydrogen may be added to depolymerizer 117 and line 125. Recyclehydrogen and light hydrocarbon free radical modifiers are removed fromcondcnsor 121 by line 126 and passed to depolymerizer 105 by line 106and depolymerizer 117 by line 136.

It is important to remember that the amount of products boiling below650 F. or below 1000" F., as the case may be, recycled to dcpolymerizers105 and 117 is critical, and must be between 20 and of the totalcomposition regardless of the distribution of the other materials. Thiscontrol is made possible by withdrawing an amount of 650 F. or 1000 F.material from the system by lines 132, 122 and 123 necessary to maintainthe proper recycle ratio. The product drawn off through lines 132, 122,and 123 is suitable as solvent for use in the chemical industry or maybe further fractionated to separate out desired solvent and aromaticfractions and if desired with recycle of the high boiling material.

The multistage depolymerization differs from single stage operation inthe processing of the high-boiling material. In the latter the recycleof the high boiling material is controlled so that the amount of thismaterial fed to The above data show that in cycles 2 and 3 theapproximate composition of 40% fresh tar, 20% 430-650 F. and 40% 650 F.+recycle is not operable because the product contains 46-47% 650 F.+material Whereas for balanced conditions the product should containabout 39.5% and 39.1%, respectively, of the 650 F.+ material. For thesystem to be in balance the 650 F.+ content of the product should beabout the same or less than the 650 F.+ recycle portion of the feed. Theconstancy of this 46-47% 650 F.+ in all operations where the total 650F.+ content of the charge to the depolymerizer (including recycle) wasequal to or greater than that of the feed is indicative that thereaction is equilibrium limited. Thus balanced conditions can beachieved by adjusting the concentrations of the 650 F.+ recycle portionof the feed to the 46-47% level. The balanced recycle condition isdemonstrated in runs 4 and 7 by the lack of build up of 650 F.+ product.These runs also show that at the same time the recycle portion of the650 F. fraction has been adjusted from 34-35% as set forth in cycles 1,2, 3, 5, and 6 to 30-31% in the balanced conditions of runs 4 and 7.

EXAMPLE 2 The experiment of Example 1 was continued for three morecycles except that no fresh tar was added and the temperature was raisedto 775 F. The data are set forth in the following table:

Cycle 8 10 Grams tar blend 470 408 Feed composition. wt. percent:

Fresh tar 0. 0.0

221-650 F. recycle 50.2 30. 9

650 F.+ recyclm.-- 49.8 69. 1 Total 650 F. content. 50.2 30. 9 Total 650F.+ content 49. 8 69. l Wt. percent 650 F.+ in produc 40 52 Wt. percentconversion 650 F.+ 18.2 24. 8 Wt. percent coke plus gas 1 l0. 10. 1

I Corrected by amount of n-hcptane lost.

The above data show that the use of 31% 650 F. recycle is more efiectivethan the higher dilution of 50%.

EXAMPLE 3 Two series of runs were made with the tar of Example 1 withand without addition of n-heptane. The following data were obtained:

HYDRODEPOLYMERIZA'IION 0F STEAM-CRACKED TAR [4 hours residence time, 765F., 1,000 p.s.i.g. H, pressure] Variable Paraiiin No addition parafiinapprox. wt. percent n-heptane in blend t. percent coke plus gas loss ontar blend The above data show that the addition of paraflin hydrocarbonsas modifiers or free-radical acceptors result in reduced coke and gaslosses after an equal number of cycles.

EXAMPLE 4 The following data obtained by the technique of Example 1illustrate the effect of n-heptane and 2,2,4-trimethyl pentane asmodifiers.

HYDRODEPOLYMERIZA'PION OF STEAM-CRACKED TAR Wt. percent gaseous prod.based on modifier 'Iypfial t1gaseous components, wt. percent gas:

n-Pentane Wt. percent (J -221 F. liqu Typical liq. components, wt.percent.:

i-Pentane 0.4-.-. 0.2.

3.9-"... 0.3. n-Hexane 315.--... 0.4. Benzene 0.5-... .4.

I Value abnormally high due to poor temperature control. Temperatureprobably higher than 775 F.

The above data show that with n-heptane as the modifier, the degradationproducts are predominantly normal, i.e. n-butane, n-hexane, whereas withiso-octane the degradation products are predominantly branched(isobutane, isopentane and unreacted feed not shown).

EXAMPLE 5 The following data obtained by the technique of Example 1illustrate the effect of branch-chain paraiiin modifiers in comparisonwith olefins of similar skeletal configuration.

BRANCHED CHAIN MODIFIERS IN HYDRODEPOLYMER- IZATION 0F STEAM-CRACKED TAR[500 p.s.i.g. H at start] Run number 93 94B Modifier, 2,4,4-tzimethylPentane Pentene-l Grams modifier 50 50 Reaction temp., F. Hours oi runPentane-Z 50 Grams modifier 10 Wt. percent gaseous prod. based modifierTypical gaseous comp, wt. percent gas n-Pentane Wt. percent (Jr-230 F.liquid, based on modifier Typical C.=.230tF. liquid pr0d., wt.

Bromine number 1 Usual designation 2,2,4 trimethyl pentane.

The above data show that saturated branch chain fragmentation productsare produced by using branched chain olefins as modifiers. Furthermore,the degradation products are branched paraflins illustrating hydrogentransfer, alkylation, isomerization and demethanation reactions.

EXAMPLE 6 The following data recapitnlated from Example 5 show theefifect of residence time in the modifier on the yield of importantproducts, particularly triptane.

HYD RODEPOLYME RIZATION 0F STEAM-C RACKED TA R [500 p.s.i.g. Hz pressureat start, single pass operation] I Usual designation 2,2,4 trimethylpentane.

These data clearly show that the important product triptane can beobtained when the modifier is a branched paraffin or olefin such asiso-octane, alkylate, di-isobutylene, etc. Actually an increase intriptane content has been observed at conditions where the modifierconsumption is so great that the yields are only indications of whatmight be achieved. The above data show that when the temperature wasreduced to 750 F. and the reaction time for 3.5 hours and higher to l,the triptane production was increased 24 fold. This underlines theimportance of a short residence time.

The above description has shown that the depolymerization of tars andother residua can be carried out in the presence of reacion modifiers orfree radical accepors to provide a process in which coke and gas isminimized and gas oil and other products are maximized.

EXAMPLE 7 A steam cracked tar consisting of 35.7% material boiling430-650 F., 34.3% boiling 650-1000 F., and 30% boiling l000 F.+ andhaving slurried therewith about 05-10% CaO was subjected to severalcycles of hydrodepolymerization for four hours each at 765 F. under 91000 p.s.i.g. hydrogen pressure while about 10% n-heptane, based on tarwas thoroughly agitated with the liquid. The following data wereobtained:

HYDRODEPOLYMERIZATION OF BATON ROUGE CRACKED TAR [1,000 p.s.i.g. Hpressure, 765 F., 4 13mg] residence time in presence of Run number 1 2 3Grams calcium oxide- 50 10 Grams tar feed 400. 4 450. 7 468. 4Composition of tar feed, Wt. p

Fresh tar 39. 6 40. 3 36. 5

430-050 F recyc1e... 20. 4 18. 3 16.5

650 F.+ recycle.-- 40. 0 41. 4 47. 0 Grams n-heptane 50. 1 50. 0 50. 0Grams nheptane consumed 20. 5 l4. 3 13. 1 Conversion 650 F.+ to 650 F,percent.. 25. 0 28.8 28. 6 Wt. percent coke plus gas loss 1 7. 4 3. 73.3

1 After correction for n-heptane consumed.

The above data shows that calcium oxide was quite efiective in reducingthe coke plus gas losses. Approximately the same results were achievedwith grams of CaO as with 50, conditions otherwise being the same.

EXAMPLE 8 The experiment of Example 7 was repeated except that clarifiedoil from catalytic cracking was used as the feed. The following datawere obtained:

HYDRODEPOLYMERIZATION OF CLARIFIED OIL [n-Heptane and lime modifiers, 4hours at 775 F., 1,000 p.s.i.g. Hz at start] Run number 4 5 6 Grams feed424. 8 437. 9 364. 5 Grams n-heptane 50 50 0 Grams lime 50 10 10 Wt.percent cenv. 34 31 30 Grams n-heptane lost 10. 7 12. 2 Coke plus gaslosses, wt. percent clarified 011.... 1. 6 1.0 4. 5

EXAMPLE 9 A steam cracked tar consisting of 35.7% material boiling430-650 F., 34.3% boiling 650-1000 F., and 30% boiling 1000 F.+ wassubjected to several cycles of hydrodepolymerization in two stages forfour hours each at 765 F. under 1000 p.s.i.g. hydrogen pressure whileabout 10% n-heptane, based on tar was thoroughly agitated with theliquid. The following data were obtained:

HYDRO DEPOLYMERIZATION OF STEAM CRACKED TAR [1,000 p.s.l.g. hydrogenpressure at start; 4 hours residence time, about 10% n-heptana on tarfeed added] Operation Balanced condition Balanced Single condition stagemultiple stage Proposed stage I I II Data from batch operation cycle- 75 11 Temperature F 765 765 775 Feed composition, wt. percent:

Fresh 8-2 tar 36. 1 39. 1 0 650 F. recycle 18. 0 20. 7 28.3 650 F.+recycle 45. 9 40. 2 3 71.7 Wt. percent 650 F.+ in produc 45. 8 46. 5 E0.9 Conversion 650 F.+ material, wt. percent. 34 29 29 Coke plus gaslosses, wt. percent 1 4. 2 0. 8 7 Coke plus gas losses, at balancedconditions wt. percent fresh 8-2 tar 11.5 1 7. 3

Est. ultimate yield, vol. effiiiih t 93 and gas.

The above description does not by any means cover the possible uses ofthis invention or the forms it may assume but serves to illustrate itsfundamental principles and an assembly in which the novel features asdisclosed have been incorporated. It is obvious that changes in thedetails may be made without departing from either its novelcharacteristics or the spirit and scope of the invention as defined inthe appended claims. For example it is within the scope of thisinvention to use a multicompartmerited reactor or combination ofreactors instead of a series of single reactors since the term stage isintended to denote a condition of concentration and only to a lesserextent one of temperature and residence time. It is also within thescope of this invention to operate depolymerizer 5 of FIG. 1 or both ofthe depolymerizers and 117 of FIG. 2 in the absence of hydrogen.

EXAMPLE 10 The foregoing data have shown that conversion or thehigh-boiling components in steam-cracked tar are affected by dilutionand by amount of low-boiling materials added as solvent and that highdilution tends to retard the depolymerization of the high-boilingcomponents to 650 F.-. The same analogy applies to conversion of thel000 F.+ material. This is demonstrated by experimental data in whichthe accumulated 650 F.+ material from previous cycles (A) was blendedwith 430650 F. solvent and depolymerized similarly to conditions in aprevious example but the product was separated into 430-650 F., 650-1000F., and 1000 F.+ product. This 1000" F.+ product was diluted with430-650 F. product from a similar depolymerization process (Run B) andwith catalytic cracking clarified oil containing predominantly 650-1000F. material and after depolymerization was separated so as to ascertainconversion of the 1000'" F.+ product. These data are summarized asfollows:

Run number 77 81 Cycle number 11 12 Tar feed, grams 8 480. 5 Source of430-650 F. recycle Comics- Run B.

lte Source of 6501000 F. recycle, run Clarified Run 77. Composition, wt.percent: Oil

Fresh steam-cracked tar 0 430-650 F. recycle 650-1000 F. recycle- 1,000F.+ recycle 48.8 Modifier:

Grams heptane Grams CaO.- Operating conditio 'Iemperature, F 775 775.Hours of run 4 4. Pressure, p.s.i.g.:

At sta 1,000. Maximum 1,050. Recoveries, grams:

Hydrocarbon modifier 27.7 42.1. Liquid err-modifier, grams:

-22 F 1.1 1.8. 221375 F. 4.2 8.6. 375-430F. B.6 35.]. 430-050 152.4140.9. 650-1 000 F-. 35.1. 120.0. 1,000 F.+ 160.2 158.9. Gas 15.8--10.8. Coke 30.8 5.0. Overall material baL, wt. percent- 100.5--- 98.7.Material bal. based on tar 103.8- 100.1. Conversions, wt percent:

650 F.+ to 650 F.- 29.0"..- 20.0. 1000 F.+ to 1000" F. 15.9-.----- 13.4

1 Refers to steam-cracked tar product and not to clarified oil solvent.1000 F.+ material from run 77 blended with catalytic clarified oil.

EXAMPLE 1 1 A feed composition similar to that used in Run 77 andconsisting of about 31% fresh steam-cracked tar 30.6% 430-1000 F.recycle and 38.4% l000 F.+ recycle from previous operation together withabout 10% hydrocarbon modifier consisting of either branched or straightchain hydrocarbons is thermally depolymerized at temperatures in therange of 750-790 F., preferably about 775 F. for residence times of 1-6hours, preferably 2-4 hours and the products are separated into 430 F.and lighter fractions, 430-1000 F. hydrocracker feed and 1000 F.+unconverted product. The latter is recycled to extinction.

EXAMPLE 12 A feed composition, similar to that used in Run 81 consistingof about 17% fresh steam-cracked tar 49.9% 430-1000 F. recycle productand 33.1% recycle 1000 F.+ product together with up to 10% hydrocarbonmodifier, and if desired with an alkaline modifier, is depolymerized attemperatures in the range of 750-790 F. preferably about 775 F. forresidence times of 1-6 hours preferably 2-6 hours and the products areseparated into 430" F. fractions, 4301000 F., and 1000 F.+ fractions.The latter is recycled to extinction. The higher dilution of Run 81,hence less fresh tar feed, has the characteristics of smaller losses tocoke and gas.

EXAMPLE 13 The foregoing examples are based upon a steam-cracked tarcontaining 30% 1000 F.+ material. Since this value may vary over wideranges a general illustration of the process in keeping with the data ofRuns 77 and 81 is a feed having composition of 1050% Fresh Tar Feed15-50% 4301000 F. Recycle 30-40% 1000 F.+ Recycle This feed isdepolymerized at temperatures in the range of 75 -790 F. for a period of1-6 hours and after separation of the 1000 F.+ portion from the 1000" F.portion the former is blended with fresh feed and 430-1000 F. diluentand recycled to extinction.

The nature and advantages of the present invention having thus beenfully set forth and illustrated and specific examples of the same givenwhat is claimed as new, useful and unobvious and desired to be securedby Letters Patent 1s:

1. A process for the thermal treatment of a hydrocarbon residuum feedhaving Conradson carbon numbers between 5 and 40 in a reaction zone toproduce low boiling products, which comprises heating said residurn andrecycled products, within the reaction zone, under a pressure sufficientto maintain the residuum in the liquid phase and at a temperaturebetween 700 and 900 F., adding hydrogen to the reaction zone whilemaintaining therein a free radical acceptor, chosen from the groupconsisting of 1-25 wt. percent of an acyclic hydrocarbon modifier,having 2 to 20 carbon atoms, 0.] to 50 wt. percent of a mild alkali, andmixtures thereof using 0.1 to 1 part by weight of alkali per par byweight of feed where mixtures thereof are utilized, removing reactedproducts, including low boiling products, and separating a portion ofthe reacted products into a high-boiling fraction and a low-boilingfraction, recycling said high-boiling fraction and said lowboilingfraction to the reaction zone at rates sufiicient to maintain a balancedcondition wherein these high boiling and low boiling fractions aremaintained in the reaction zone at about the same level of concentrationas these fractions are present in the residuum feed introduced to thereaction zone, the low boiling fraction constituting between 20 and 50%of the total feed composition, inclusive of the amount thereof recycled.

2. The process of claim 1 wherein the residence time of the acyclichydrocarbon modifier within the reaction zone is one hour or less, andthat the residua-recycle mixture is 1 to 6 hours.

3. The process according to claim 1 in which the balanced condition isachieved with a recycle of the high boiling fraction of 46-47%.

4. The process of claim 3 in which the residence time of the acyclichydrocarbon modifier in the reaction zone is one hour or less, and thatof the residue recycle mixture is 1 to 6 hours.

5. The process of claim 1 in which the low boiling fraction boils below650-1000" F. and the high-boiling fraction boils above 650-1000 F.

6. The process of claim 1 in which the low-boiling fraction boils below650 F. and the high-boiling fraction boils above 650 F.

7. The process of claim 1 in which the low-boiling fraction boils below1000 F. and the high-boiling fraction boils above 1000 F.

8. The process of claim 1 in which the alkali is CaO.

9. The process of claim 1 in which the deploymerization is carried outin the presence of hydrogen added to the reaaction zone in concentrationranging from about 50 to 5000 s.c.f. per barrel of feed.

10 The process of claim 1 wherein from about 0.1 to

10 wt. percent of an alkaline material, based on total feed, ismaintained within the reaction zone during the thermal treatment of thehydrocarbon residuum feed. 11. A process for the thermal treatment of ahydrocarbon residuum feed having a Conradson carbon number between 5 and40 which comprises heating said residuum feed in a first reaction zonein the presence of hydrogen added in concentration ranging from about 50to 5000 s.c.f. per barrel of feed, under pressure suflicient to maintainthe residuum in the liquid phase and at a temperature between 700 and900 F. in the additional presence of l to 25 wt. percent of an acyclichydrocarbon modifier, having 2 to 20 carbon atoms, removing reactedresiduum from said first reaction zone, and passing a portion of itstogether with an acyclic hydrocarbon modified to a second reaction zoneunder conditions more severe than in said first reaction zone, saidsecond reaction zone being operated at a pressure sufficient to maintainthe residuum in the liquid phase, and at temperature ranging between 750to 950 F., combining the reaction products from both reaction zones,separating the reaction products into a high-boiling fraction and alow-boiling fraction, recycling the low-boiling fraction to each of saidreaction zones such that the feed to the two reaction zones contains 20to 50% of low-boiling material exclusive of the modifier, and recyclingsuflicient of the high-boiling fraction to the two reaction zones sothat the high-boiling recycle from the combined reaction zones is equalto the recycle portion in the feed to the first zone.

12. A process for the thermal treatment of a hydrocarbon residuum feedhaving Conradson carbon numbers between 5 and 40 which comprises heatingsaid residuum feed in a first reaction zone in the presence of hydrogenadded in concentration ranging from about 50 to 5000 s.c.f. per barrelof feed, under a pressure sulficient to maintain the residua in theliquid phase and at a temperature between 700 and 900 F. in theadditional presence of 1 to 25 wt. percent of an acyclic hydrocarbonmodifier, having 2 to 20 carbon atoms, removing reacted residuum fromsaid first reaction zone and separating said residuum in a firstseparation zone into a low-boiling fraction and a high-boiling fractionand passing a. portion of said low boiling fraction to a secondseparating zone, and said highboiling fraction to a second reactionzone, heating said residuum in said section reaction zone in thepresence of hydrogen added in concentration ranging from about 50 to 500s.c.f. per barrel of feed, under more severe conditions than in thefirst reaction zone and under a pressure sufficient to maintain theresiduum in the liquid phase, and in the additional presence of anacyclic hydrocarbon modifier having 2 to 20 carbon atoms, removingreacted residuum from said second reaction zone and passing it to saidfirst separation zone, removing a portion of said lowboiling fractionfrom said second separation zone as product and recyling an amount ofthe remainder to said first and said second reaction zones such that thefeed to the two reaction zones, contains 20 to 50% of the low-boilingmaterial exclusive of modifier, and recycling a portion of 13 a fractionboiling above 650 F. to said reaction zones so that the high-boilingrecycle from the combined zones is equal to that in the feed to thefirst zone.

13. The process of claim 12 in which the low-boiling fraction boilsbelow 650-1000 F. and the high-boiling fraction boils above 650-1000 F.

14. The process of claim 12 in which the low-boiling fraction boilsbelow 650 F. and the high-boiling fraction boils above 650 F.

15. The process of claim 12 in which the low-boiling fraction boilsbelow 1000 F. and the high-boiling fraction boils above 1000 F.

16. A process for the thermal treatment of hydrocarbon residuum havingConradson carbon numbers between and 40 which comprises heating saidresiduum in the presence of hydrogen in a first reaction zone under apressure sufiicient to maintain the residuum in the liquid phase and ata temperature between 700 and 900 F. in the additional presence of l to2.5 wt. percent of an acyclic hydrocarbon modifier, having 2 to 20carbon atoms, removing reacted residuum from said first reaction zone,and passing it to a second reaction zone under more severe conditionsthan in said first reaction zone, under a pressure sufiicient tomaintain the residuum in the liquid phase, combining the reactionproducts from both reaction zones, separating the reaction products intoa fraction boiling below 650 F. and a fraction boiling above 650 F.,recycling the fraction boiling below 650 F. to each of said reactionzones such that the feed to the two reaction zones contains 20 to 50% oflow boiling material and recycling all of the high-boiling fraction tothe second reaction zone.

17. A process for the thermal treatment of hydrocarbon residuum havingConradson carbon numbers between 5 to 40 which comprises heating saidresiduum in the presence of hydrogen in a first reaction zone under apressure sulficient to maintain the residuum in the liquid phase and ata temperature between 700 and 900 F. in the additional presence of l to25 wt. percent of an acyclic hydrocarbon modifier, having 2 to 20 carbonatoms, removing reacted residuum from said first reaction zone, andpassing it to a second reaction zone under more severe conditions thanin said first reaction zone, under a pressure sufiicient to maintain theresiduum in the liquid phase, combining the reaction products from bothreaction zones, separating the reaction products into a fraction boilingbelow 1000 F. and a fraction boiling above 1000 F recycling the fractionboiling below 1000" F. to each of said reaction zones such that the feedto the two reaction zones contains 20 to of low-boiling material andrecyling all of the high-boiling fraction to the second reaction zone.

18. The process of claim 12 in which the conversion in both the firstand second reaction zones is carried out in the presence of hydrogen.

19. The process of claim 13 in which the conversion in both the firstand second reaction zones is carried out in the presence of hydrogen.

References Cited UNITED STATES PATENTS 1,770,287 7/1930 Pelzer 208-1062,031,336 2/ 1936 Smith 208-76 2,748,061 5/ I956 Olberg et a1 208-763,147,206 9/ 1964 Tul'leners 208-5 6 3,472,760 10/ 1969 Paterson 20886DELBERT E. GANTZ, Primary Examiner G. E. SCHMITKONS, Assistant ExaminerU.S. Cl. X.R.

